Interventional radiology and interventional neuroradiology are medical disciplines expanding minimally invasive treatments for vascular defects and vascular malformations while avoiding the cost and burden of open surgery. Clinicians utilize various imaging modalities (primarily fluoroscopy) along with percutaneous (vascular access) guide and delivery catheters to routinely conduct vascular “stenting” to open or maintain patency of a diseased vessel lumen and vascular occlusion or embolization to stop the blood flow in a vessel or isolate a vascular area from blood flow.
Peripheral vascular (PV) intervention treatments include vascular occlusion for treating hemorrhages, aneurysms, and tumor isolation, including nephroma, hematoma, peripheral aneurysms, and other vascular malformations, and uterine fibroids among other conditions. Interventional neuroradiology (INR) treatments include treating cerebral vascular malformations such as arteriovenous malformations (AVMs) wherein the artery and vein are connected and a variety of cerebral aneurysms or bulging and weakening of a vessel wall. Vaso-occlusive (V-o) devices are used to isolate and/or fill the defect. Other INR procedures include occlusion of ateriovenous fistulae (AVF), parent vessel sacrifice (PVS), and tumor indications among other conditions.
The V-o devices can take a variety of configurations, and are generally formed of one or more members that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used V-o device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. Some known anatomically shaped V-o devices form into a shape of an anatomical cavity such as an aneurysm and are made of a pre-formed strand of flexible, biocompatible material such as stainless steel, platinum, or a shape memory alloy, e.g., a nickel-titanium alloy (NiTinol). Such V-o devices comprise one or more members formed in a generally spherical or ovoid shape in a relaxed, or deployed state and the device is sized and shaped to fit within a vascular cavity or anomaly, such as for treatment of aneurysm or fistula. The V-o members are first formed in a generally linear fashion as a helical winding or braid. The generally linear V-o member is then configured and captured around an appropriately shaped mandrel or form and heat-treated so that the V-o members retain the complex shape in the relaxed or deployed state. The V-o device is then manipulated within its elastic deformation range into a less complex, generally straight, shape, i.e., its pre-deployed state, for insertion through a cannula and catheter. As such, the V-o member is a helical winding or braid on which a complex secondary shape is imposed.
Delivery of such a coil in the treatment of aneurysms or other types of arteriovenous malformations can be accomplished by a variety of means, including via a catheter in which a series of single coil devices is pushed through the catheter by a pusher to deploy the coil. The coils pass through the lumen of the catheter in a linear shape and take on a complex shapes as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the single coil from a pusher have been developed. To complete an occlusion procedure, the physician must sequentially reload the catheter with several individual coils until it is determined the occlusion is sufficient. This physician typically determines whether sufficient coils have been deployed by assessing the level of occlusion of the vessel flow or by evaluating the density of the coil packed into the aneurysm sack (i.e., the coil pack), both performed by typical medical imaging techniques. This “place and assess” method can extend the time and cost of the medical procedure and also can increase the imaging exposure (i.e., radiation exposure) to both the patient and the physician.
There are many known variations of metal embolic coils including those with offset helical and twisted shapes having multiple axially offset longitudinal or focal axes with a secondary shape having coiled ends and a middle loop. A stretch-resistant V-o coil is also known that is formed from a helically wound primary coil and a stretch resistant member, that can also have a secondary shape with coiled ends ad a middle loop, and an embolization coil having a single closed loop. Highly flexible coils with secondary shapes are also known that form occlusive implants that are sufficiently flexible that each can be folded upon itself and maintain that configuration. It has been found that single strands of small diameter nickel-titanium alloys, as well as other metal alloys, used to form metal V-o coils can be kinked if twisted and pulled as can occur during or after deployment from a catheter, especially if the doctor wishes to withdraw a partially deployed coil because it is somehow incorrect in size, shape, or length to effect the desired repair. Other coils utilize multiple strands of small diameter metal alloy wire to overcome this limitation. However, all of these methods of construction rely upon a costly metal alloy and significant processing costs to fabricate the embolic coil.
Wire wound coils can be further enhanced through coating and/or fiber attachment to induce specific tissue or thrombus response. However, the mechanical performance of these devices is limited by the single material properties of the base wire and the fabrication techniques associated with wire forming.
For larger vessel occlusion, metal wire coils present significant limitation and/or require a significant number of devices to achieve suitable vessel occlusion. Other, non-coil devices are known that may utilize an articulating mesh structure fabricated from similar metal alloys and wire-forming methods. While these devices can effectively occlude larger vessels, they are similarly very expensive and have proven to be challenging for the physician to place accurately due to the length of their pre-deployed state.
Traditional polymers that are not shape memory polymers cannot provide suitable “shape fixity” after storage in a stressed condition for extended periods. Traditional polymers suffer from “creep” resulting in a loss of shape fixity.
Polyester fibers and braiding have been added to the wire devices as a means to enhance thrombogenic response. Some coils are coated with a bioabsorbable polymer (PLGA, etc) as a means of enhancing blood/tissue interaction. Other coils are coated with a hydrogel to cause them to swell in-situ and provide a tighter coil pack. However, all of these products rely on an underlying metal coil design. Typically resilient materials such as shape memory metal alloys or superelastic metal alloys are used to maintain the unique coiled sample post deployment while the device is being held in a straight configuration inside of a coil holder (tube/hub device) that allows easy physician loading into the proximal end of the delivery catheter. Again, these devices suffer performance limitations and high cost constraints due to the underlying materials of construction.
The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention is to be bound.